THE COLLAR-CELLS OF HETEROCGLA. 17 
Flagellum. 
In the living 8. compressum, the flagellum may be 304 
to 504 long. The movement is certainly asymmetrical, with 
a longer rest on one side than on the other.!' In several cases 
it was also certain that the motion lay entirely in one plane. 
It is rare to see flagella moving more rapidly than about 10 
beats to the second. I have guessed the greatest rapidity I 
observed to be 15 or 20 beats to the second. The thickness 
in life was estimated at tu to +>; it appeared uniform, 
except sometimes for a thickening of the part inside the 
collar. In paraffin sections this thickening is also found, in 
perhaps a third of the cells; it does not extend for more than 
about 1 from the intra-choanal surface, the thickness above 
this point being uniform, and measured in different flagella from 
15. to°3. But in the paraffin sections the flagellum can be 
traced inside the substance of the cell to the nucleus (cf. cut, c), 
and in the osmic preparations stained in bulk it is not wider 
here than in its terminal portion. For greater definiteness I 
shall term the part of the flagellum below the general outline 
of the cell the radix of the flagellum. 
Intra-choanal Area. 
It has been stated above that the outline of the intra-choanal 
area is in life less definite than that of the sides of the cell. 
Vosmaer and Pekelharing mention carmine experiments which 
hint that here, as supposed by the early authors, food is taken 
in; and it will be seen below that careful examination of my 
own permanent preparations is far from contradicting this view. 
Tn life, neither ingestion nor egestion were ever witnessed ; 
but in a sponge which had been two hours in a basin of sea 
water, after two hours’ exposure at low tide, almost every cell 
1 Minchin states this very definitely for Leucosolenia coriacea (16, 
p. 264). I have also a note that the same holds good for Leucandra 
aspera and another sponge (I think S. raphanus). These four are all 
sponges with tubular or thimble-shaped chambers ; it is possible that the beat 
is symmetrical in short hemispherical chambers where the axis of the collar- 
cell is nearly parallel to that of the chamber. 
vou. 38, PART 1.—NEW SER. B 
